The intestinal epithelium is a single layer of cells that protects the host from the harsh environment ofthe gut lumen. In inflammatory bowel disease (IBD), this important barrier function is compromised in association with excessive activation ofthe mucosal immune system. Intestinal dendritic cells (DCs) and gamma delta T-cells have an immunosuppressive effect through the production of interleukin (IL)-IO and TGFbeta;however, the role ofthese immune cells in regulating and maintaining epithelial barrier function remains poorly understood. Reports from the literature indicate that both DCs and gamma delta T-cells express junction proteins and maintain close contact with intestinal epithelium. My long-term objective is to determine the requirement for epithelial-immune cell interactions in regulation of epithelial function in the context of IBD. The central hypothesis of this application is that gamma delta T-cells and dendritic cells directly interact with the intestinal epithelium to maintain mucosal homeostasis and prevent disease. The majority of methods used in this study will allow direct analysis of epithelial-immune cell interactions both in co-culture models in vitro, in vivo models of disease and live imaging analysis. The first aim will investigate the requirements for DC junction protein expression in dendrite extension and whether DC modulation of barrier function contributes to disease. Dendrite extension and junctional complex interactions between epithelial and DCs will be assessed through both traditional in vitro methods in co- culture with isolated mouse DCs and polarized mouse colon epithelial cells, and in vivo using transgenic mice expressing fluorescent-tagged junction proteins. Further studies will be performed to deplete DCs in mice with a known barrier defect to determine the contribution of DCs in immunosurveillance and mucosal homeostasis in response to barrier dysfunction. The second aim will determine how gamma delta T-cells contribute to the maintenance and regulation of epithelial barrier function. An in vitro co-culture model will be used to investigate epithelial and gamma delta T-cell interactions in the regulation of barrier function. In addition, mice either deficient in gamma delta T-cells or expressing a gamma delta T-cell-specific GFP transgene will be used to assess the effect of gamma delta T-cells in the maintenance of barrier function during mucosal homeostasis and disease initiation. PUBLLIC HEALTH RELAVENCE: Completion of these aims will have significant positive effects on human health and increase our understanding of how resident immune cells contribute through signaling pathways or direct interaction with the intestinal epithelium to promote mucosal homeostasis. These findings may identify novel therapeutic targets for the treatment of IBD.